186 PROTOZOAN PARASITISM 



in one end of the cyst, in the single organism, but 

 commonly are four in number, usually all grouped 

 but at times two in one end and two in or toward the 

 other. The fibrils of the flagellar apparatus are 

 twisted and wavy lines, to be studied by the very care- 

 ful investigator. The cyst is, therefore, a multiplica- 

 tion cyst as well as a resistant phase. It is readily 

 stainable and its structure recognizable. For more 

 minute structural detail the reader is referred to 

 works, such as by Wenyon (1926), dealing more at 

 length and minutely with such matters than is here 

 desirable. 



The organism divides within the cyst, by binary 

 fission, after mitosis of the nuclei, and two offspring 

 are liberated at excystment, on reaching its natural 

 habitat. Similar longitudinal division has been de- 

 scribed in the active form and this probably occurs 

 within the intestine, since excystment in the same 

 individual does not seem likely. Under conditions 

 of observation of the parasite from duodenal con- 

 tents and liquid stools division is not apt to be seen. 

 Cultivation of the organism has not been done 

 and its reproduction has not been extensively fol- 

 lowed. 



The cytoplasm is of alveolated, finely granular 

 character, the dorsal part more dense than the ventral. 

 It is not vacuolated or filled with bacteria as in the 

 other flagellates. Evidently its food is taken in solu- 

 ble form and the materials have not yet been supplied 

 properly for the growth in culture. 



